The curvature of dislocation lines can serve as a probe for the resolved shear stress in multianvil deformation experiments. This method is very well adapted to deformation experiments in the multianvil apparatus where the microstructure (and in particular the dislocation density) can be largely determined by early deformation stages. On the contrary, individual dislocation movements can adjust more rapidly to stress level changes and can thus record the last stress level borne by the specimen before it is quenched. The method has been applied to dense specimens of wadsleyite and ringwoodite deformed at 15 to 22 GPa and 1000 to 1500--1600¿C. The resolved shear stress is very similar in wadsleyite (400 MPa) and ringwoodite (350 MPa) deformed at 1000¿C showing that these minerals exhibit very similar rheological properties under these conditions.